成层土中载体桩承载力特性实测研究

Research on the bearing capacity characteristics of ram-compacted piles with bearing base in layered soil based on measured data

载体桩在成层土中的承载力特性尚未得到有效的分析。以成层土分布较为典型的苏州地区为例,采用统计方法分析该地区浅层土体物理力学特性,得到适合作为载体桩持力层的地层特性,分析得到单桩承载力在各持力层中的通用公式,同时得到载体填充量的一般公式,对单桩及群桩基础的载体填充量进行计算并验证,以开挖实测得到载体的合理抗拔半径,总结成层土中影响载体桩质量的因素及相应对策。结果表明,除个别较软弱土层外,一般地层均适合作为载体桩的持力层;各适用土层单桩承载力与持力层深度呈现近似抛物线关系;粉土、粉砂作为载体持力层时对单桩承载力提高效果明显;各土层载体填充量也可统一列式求解,单桩载体填充量上限为2.3m^(3),群桩载体填充量上限为1.8m^(3);水泥砂拌合物外边界可作为抗拔计算半径;无明显低应变反射信号的载体桩性能应采用综合分析或其它原位测试方法进行验证。

The bearing capacity characteristics of ram-compacted piles with bearing base in layered soil have not been analyzed deeply.Taking the typical layered soil in Suzhou area as the research object,the physical and mechanical properties of the shallow soil in this area were analyzed by statistical methods.The generalized equations of bearing capacity of single pile in each bearing stratum and filling volume were obtained.The filling volume of single pile and pile groups were calculated and verified.The reasonable anti-pulling radius was obtained through excavation.The factors affecting the quality of ram-compacted piles with bearing base in layered soil and countermeasures were summarized.The results show that the bearing layers of ram-compacted piles are suitable except for a few types of soft soil layers.The single pile bearing capacity of each applicable soil layer and the depth of the bearing layer present an approximate parabolic relationship.The effect of silt and sand layer as bearing layer on improving the bearing capacity of single pile is obvious.The filling volume of each soil layer can also be solved by the unified formula.The upper limit of filling volume in single pile is 2.3 m^(3),while in the pile group is 1.8 m^(3).The outer boundary of cement-sand mixture can be used as the anti-pulling radius for pullout resistance.The performance of ram-compacted piles with bearing base without significant low-strain reflection signals should be verified by comprehensive analysis or other in-situ testing methods.